WASHINGTON - Climate-warming carbon emissions from new cars and light trucks in the United States dropped 3 percent in 2005, the first decrease in nearly two decades, Environmental Defense reported Thursday.

"We see some signs of good news here," said the group's Jon DeCicco in a telephone news briefing announcing the findings.

High fuel prices and tighter fuel efficiency standards for light trucks have helped push down carbon emissions, the report said.

Gasoline prices topping $3 in 2005 also affected how much people drove: growth in the amount of driving averaged 2.3 percent each year from 1990 to 2004, but was less than 0.2 percent in 2005.

Growth in carbon dioxide emissions from U.S. vehicles, which grew at a steady 2 percent per year from 1990 to 2004, was less than 0.4 percent in 2005. This included not just new cars, but all of the approximately 200 million cars and light trucks in use on U.S. roads.

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The report also measured the so-called carbon burden of the 12 U.S. vehicle manufacturers, which was billed as a way to measure their impact on global warming. The carbon burden was calculated by looking at how efficient vehicles are, how carbon-rich their fuel is and how many new vehicles individual companies sell.

THE BURDEN OF CARBON

The six largest manufacturers had the biggest carbon burdens. General Motors and Ford saw their carbon burdens decline from 1990 through 2005, a consequence of shrinking market share, according to the report.

Greg Martin, a spokesman for General Motors, said the report reflects that his company sells the most vehicles in the United States, and noted that improvement in its emissions numbers was expected.

"We've made very good progress in the last several years but we would expect to see that rate improve at a much more quick pace as we have a product plan that's based on more diverse and clean fuels," with eight hybrid vehicles expected to be on the market by year's end, Martin said by telephone.

DaimlerChrysler had its carbon burden rise more than 60 percent over the period, with sales rising more than 50 percent.

Toyota, ranked fourth among U.S. automakers, saw its carbon dioxide emissions drop by 3 percent, but its carbon burden grew by 125 percent, an increase attributed entirely to increased sales.

BMW, ranked 10th, was a "success story," DeCicco said, noting that it had grabbed more of the market and cut carbon dioxide emissions by more than 12 percent over the period. This was due to improved efficiency overall and the introduction of the sub-compact Mini Cooper, the report said.

The full report is available online at www.environmentaldefense.org/carbonburdens.